The present invention relates to a rubber composition for coating a belt layer steel cord, which inhibits separation from the steel cord.
Conventionally, adhesion to the steel cord is required in rubber compositions that coat the steel cord of a belt layer. In order to improve adhesion, the methods of compounding, for example, cobalt salt, silica or resin in the rubber component are known. However, even when these components are compounded in a rubber composition, adhesion with the steel cord is insufficient and there is the problem that the rubber composition separates from the steel cord by running.
In order to solve such problems, disclosed are a rubber composition for a steel belt containing a radical chain inhibitor (JP-A-2003-313369) and a rubber composition for coating a belt layer steel cord containing a special carbon black (JP-A-7-258470). However, because the amount of sulfur is large in both cases, there is the problem that the sulfur crosslinking density increases and the rubber becomes hard (tensile strength at break and elongation at break decrease) when thermally oxidized and degraded.